For iteratively reconstructing an image from projection data, which can be acquired by using a computed tomography system, in an iteration step a forward projection through an actual image can be performed for generating simulated projection data, a difference between the simulated projection data and the acquired projection data can be determined, and the difference can be backprojected for updating the actual image. Several of these iteration steps can be performed, until a termination condition is fulfilled.
The forward projection can be implemented as disclosed in the article “An Improved Algorithm for Reprojecting Rays Through Pixel Images” by P. M. Joseph, IEEE TMI, MI-1, pages 192-196 (1982), wherein the image is divided into image elements arranged in a rectangular grid and wherein an interpolation kernel is used for interpolating image elements arranged along a line being parallel to a main axis of the grid for calculating interpolated values located on rays along which the forward projection is performed. The interpolated values, which are located on a same ray, are summed for generating a projection value. Projection values determined for several rays form the simulated projection data.
The iterative reconstruction using the above described forward projection may lead to image artifacts, thereby decreasing the quality of the reconstructed image.